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DOES A THERMOS require tevilas keilim?
Yes. Even though the outside is plastic, the inner lining that touches the food or liquid is usually metal. It requires tevilah with a brocha.
Can I pour soup or hot water into a thermos on Shabbos? I want to bring it out to my Sukkah and keep it warm. Since the thermos is designed to retain heat, is there a problem of hatmanah (insulating)?
A thermos may be used on Shabbos for several reasons:
- It is treated as a kli sheini (second vessel), and hatmanah is permitted in such cases.
- At the time of pouring, the thermos is uncovered; closing it with a lid is considered sealing a container, not insulating.
- The insulation is built into the thermos walls, unlike classic hatmanah, which involves wrapping a vessel.
However, according to Igros Moshe, one should not wrap a thermos in towels or blankets on Shabbos, as some opinions consider that hatmanah.
